1. Field of the Invention
This invention relates to a level-variable supporting apparatus.
2. Description of the Prior Art
When a sick person remains confined to his bed for a long time, decubitus will occur. Decubitus is a state in which ulcer is formed as follows: since the patient is laid prolongedly in bed with a substantially fixed posture, certain regions of his body continue to be pressed by the underlying bedclothes, causing the blood capillaries of the regions to be compressed: and this leads to the impairment of subcutaneous blood circulation and further to the necrosis of tissues, thus resulting in the development of ulcer. An internal pressure of blood capillaries is about 25 mmHg, and if an external pressure higher than this value is given for many hours, the above mentioned circulatory disorder readily occurs. Decubitus is also called bedsore, which gives a great pain to the sick person. Especially in a sick person who is prostrated and poorly nourished, decubitus develops within a short period of time.
Attempting to prevent the development of decubitus in such a manner that only certain regions of the body are not strongly pressed for many hours through contact with bedclothes, the following various proposals have been made to date.
It was proposed that by selectively feeding air to many air chambers, these air chambers are selectively inflated to change the pressed regions of the body (Japanese Patent Publication Open to Public Inspection No. 20173/1977; Japanese Patent Examined Publication No. 40296/1985). These methods involve the problems that the apparatus becomes large in size because an air compressor and many valves are required and that sleep is disturbed by sounds from the opening and closing of valves, the exhaust of air, and the operation of the air compressor.
Another proposal is a highly cushiony pad which is packed with polyurethane gel or polyvinyl gel (Japanese Patent Publication Open to Public Inspection No. 38118/1980 or No. 159847/1982). This pad is to evenly distribute the pressure that the body receives from the pad. Due to its highly cushiony property, the above pad makes a bed all the more uncomfortable to sleep in and, moreover, the development of decubitus cannot be completely prevented in the state of evenly distributed pressure.
Further to the above mentioned proposals, a bed was proposed in which, with shape memory alloy springs incorporated, these springs are selectively heated to change the distribution of pressure (Japanese Patent Publication Open to Public Inspection No. 129021/1984). It will, however, cause an increase in the production cost to use many shape memorial alloy springs in the above case.
Other than the above mentioned apparatuses for prevention of decubitus, there are those supporting apparatuses which support a supported object so as to be movable in upward and downward directions, such as a screw jack and a rack and pinion jack, which utilize screws, racks, and gears, and a hydraulic jack utilizing oil hydraulics or hydraulic pressure. These jacks are inappropriate depending upon the type of the supported object due to noise or vibration produced by the jacks themselves, or are untoward at a place requiring cleanliness because of environmental contamination caused by oil or water leakage. In addition, a screw jack or a rack and pinion jack needs a reduction gear to reduce the speed of its upward or downward movement. A supporting apparatus which has solved these problems may be a supporting apparatus which utilizes the return of the shape memory alloy to its original shape, but still addressing a problem that such a method allows the shape of the supporting portion to lack freedom. An attempt to create a supporting apparatus which overcomes the above mentioned problem will result in a complicated structure, causing the apparatus to be difficult to handle and costly as well. A desirable supporting apparatus, which is to be used in a clean environment and also to support a sick person or a supported object which is in danger of deteriorating its quality due to vibration, is an apparatus that has a simple structure, is easy to handle, can allow the supported object or sick person to gently move upward and downward without generating vibration or noise, and, moreover, does not contaminate the environment. At present, however, such an apparatus has not yet been developed.